Electronic switch



Patented Aug. 26, 1947 ELECTRONIC SWITCH John Kelly Johnson, Deer-field, 111., assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application May 27, 1942, Serial No. 444,732

13 Claims.

The present invention relates to electronic switches and, particularly, to such switches of the mu1ti-stage or multi-unit type. In greater particularity, the invention relates to a multistage electronic switch wherein the stages are successively controlled in a predetermined control sequence.

Electromechanical switches have inherent limitations and disadvantages which render them unsuitable for numerous applications. For example, such switches consume power from the circuit which controls them, are subject to definite limitations on the speed with which they can be operated both to circuit-closingand circuitopening positions, are frequently more noisy than is desired, are subject to chattering and burning of their contacts, and may fail in operation due to dirt or other foreign matter which becomes lodged between their contacts. Electronic switches, on the other hand, may be operated substantially instantaneously, require no appreciable power consumption from the circuit which controls them, are quiet, positive,- and reliable in operation, and for many applications possess numerous other advantages over electromechanical switches.

It is frequently desirable that an electronic switch be of the multi-stage type, that the several stages thereof be cascade-connected, and that the switch as a whole be under the control of one or more master control circuits and the switching stages under the control of one or more secondary control circuits. Where only one such master control circuit is used, it is frequently desirable that only selectable portions of the switching stages be controlled by such circuit, as by connection of the latter to a selected point in the electronic switch. Additionally, it may be desirable that the switching stages be successively controlled by the secondary control circuit, the successive control of the switching stages occurring at regular or irregular time intervals, as desired. Where only one secondary control circuit is used, it is frequently desirable that such control circuit be connected to all of the switching stages but that it be effective only 6n the stage or stages which have been conditioned for operation by the master control circuit or circuits.

It is an object of the present invention, therefore, to provide a new and improved electronic switch which possesses one or more of the desirable features hereinbefore set forth.

It isan additional object of the invention to provide a new and improved electronic switch of the type described having a simple circuit arrangement involving a minimum of circuit components and one which is characterized by a h degree of stability and reliability of operation.

In accordance with the invention, an electronic switch comprises a plurality of vacuum tubes coupled in cascade, means intercoupling the tubes in groups to vary through a complete cycle the conductance characteristic of at least one tube of each group in response to impulses successively individually applied to two tubes of said each group, and means for conditioning one of the cascaded tubes to initiate a control sequence. The switch includes means for applying impulses to the aforesaid conditioned tube and to a corresponding tube of each of the groups, the im- Pulses being effective to vary the conductance characteristic of at least the aforesaid one tube of each of the successive groups of the tubes in like manner, thereby to complete successive steps of the aforesaid control sequence. The electronic switch additionally includes a plurality of output circuits each individually coupled to at least the said first-named one tube of each of the groups and adapted successively to have the energization thereof modified during the cycle of variation of the conductance characteristic of the said first-named one tube of the group of tubes associated therewith.

In accordance with a particular form of the invention, an electronic switch of the type described comprises means intercoupling the tubes in pairs to vary the conductance characteristic of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair. The switch includes means for conditioning one of the cascaded tubes to initiate a control sequence, and means for applying impulses to the said conditioned tube and alternate tubes therefrom in the cascade connection, the impulses being effective to vary the conductance characteristic of successive pairs of the tubes in like manner, thereby to complete successive steps of the aforesaid control sequence. The switch additionally includes a plurality of output circuits each individually coupled to at least one tube of each of the pairs an adapted successively to have the energization thereof modified during the cycle of variation of the conductance characteristic of the pair of tubes associated therewith.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, Fig-1 is a circuit diagram, partly schematic. of a complete electronic switch embodying the invention; and Fig. 2 is a graph used as an aid in explaining the operation of the invention.

Referring now more particularly to Fig. 1, there is represented, partly schematically, a complete electronic switch embodying the present invention in a preferred form. This switch is of the multi-stage type and includes three switching stages A, B and C. Each of the switching stages includes similar circuit components in a similar circuit arrangement and hence only the switching stage A will be described in detail, the circuit elements of switching stages B and C which correspond to similar circuit elements of the switching stage A being designated by similar reference numerals primed and double primed, respectively.

The electronic switch includes a plurality of vacuum tubes, preferably vacuum-tube repeaters, in, II and I2 in switching stage A, Ill, II and 12 in stage B, and I, II" and I2" in stage C. In .stage A, the vacuum tubes In and II are energized from a source of space current, indi-' cated as +13, through anode load resistor l3, l4, respectively, and are connected in cascade as direct current amplifier devices by a connection of the control electrode of vacuum tube ii to the junction of resistors I and II which are connected as a voltage divider, in series with a source or control electrode bias C, betweenthe anode of tube Ill and ground. The vacuum tube II is provided with a cathode load resistor l8, and the switching stages A, B and C are coupled in cascade by condensers i9 and 20 which couple the control electrode of the first vacuum tube of a succeeding stage to the cathode resistor of the second vacuum tube of a preceding stage- The vacuum tubes ill to H", inclusive, of the electronic switch are thus all coupled or connected in cascade.

The; electronic switch includes means intercoupling the tubes in groups, there being one ,such group for each of the switching stages A, B and C, to vary through a complete cycle the conductivity or transconductance of at least one tube in each group in response to impulses successively individually applied to two of the tubes of each of said groups. By the term variation of conductivity or' transconductance through a. complete cycle as used in this specification and the appended claims is meant that the conductivity or transconductance of a tube varies from a given value to another or other values but ultimately returns to its initial given value to complete the cycle of change of conductivity or transconductance. The last-named intercoupling means essentially is resistive means comprising,

in stage A, resistors l6 and 2| which are serially connected as a voltage divider in series with the bias source C between the anode of tube II and ground, the control electrode of vacuum tube l0 being coupled to the junction of resistors i6 and 2|, thus intercoupling the vacuum tubes In and II in a backward direction as direct current amplifier devices, that is, in the direction from tube II to tube l0.

The electronic switch also includes means for conditioning one of the cascaded tube to initiate a control sequence. This means, in the particular arrangement shown, comprises a control circuit including control-circuit terminals 22, 23 which is coupled through a condenser 24 to the control electrode of vacuum tube l0 by'which to apply to this tube a control impulse, thereby to change in opposite senses the conductances of tubes l0 and H effectively to condition tube H to initiate a control sequence. Thi control circuit will hereinafter be referred to as the master control circuit since it is the potential impulse thereof which determines the moment at which the control sequence of the electronic switch is initiated. For purposes of illustration, this master control circuit is shown as comprising one'output circuit of a separator system 25. The latter may be of the type shown in Television Engineering by J. C. Wilson (1937), page 347, Fig. 211, and may include integrating and difierentiating networks and has an input circuit comprising input-circuit terminals 26, 21 to which is applied a periodic potential of rectangular pulse wave form including master control pulses of relatively long duration and secondary control pulses of relatively short duration.

The electronic switch additionally includes means for applying impulses to the aforementioned conditioned tube, that is, the second vacuum tube ll of the switching stage A, and to a corresponding tube of each of the groups included in switching stages B and C to vary the conductivity or transconductance of tube of such suctube ii in the cascade connection. This lastnamed means comprises a second control circuit including control-circuit terminals 28, 29, and hereinafter referred to as the secondary control circuit, which is coupled to the control electrodes of vacuum tubes II, II, and H" by respective condensers 30, 30', and 30 having relatively small values of capacitance. The secondary control circuit comprises a second output circuit of unit 25 and is effective to apply secondary control impulses simultaneously to the control electrodes of the vacuum tubes to which it is coupled. This control circuit is preferably of the low-impedance type; that is, the impedance of the circuit internal of unit 25 between the terminals 28, 29 has a relatively low value of impedance.

The electronic switch also includes a plurality of output circuits individually coupled to at least one tube of each of the groups of tubes and adapted successively to have the energization thereof modified during the cycle of variation of the conductivity or transconductance of such one tube of the group of tubes associated therewith. In the switching stage A, for example, the output circuit comprises output-circuit terminals 3|, 32 which are coupled to the cathode resistor i8 of the second vacuum tube H through the vacuum tube i2, This output circuit is energized from a signal-input circuit comprising input-circuit terminals 33, 34which is coupled to the control electrode or vacuum tube [2 through a condenser 35. The signal source, not shown, which is coupled to the terminals 33, 34 preferably has an impedance large in comparison with the value of resistor l8. The vacuum tube I2 is energized from a space current source indicated as +13 through an anode resistor 36. The vacuum tube [2 normally is biased to anode current cutoff by a bias applied to its cathode from a bias source indicated as +C. An isolating'resistor 31, having a value large in comparison with that oi. the oathode resistor I8 is included in circuit between the cathode circuit of tube II and both the signalinput terminals 33, 34 and the control electrode of tube I 2 to prevent the application of the input signal to any of the other vacuum tubes 01 the switching stages.

Considering now the operation of the electronic switch just described, the periodic potential of pulse wave form, represented by the curve of Fig. 2, which is applied to the input circuit 26,21 of unit 25, includes periodic master pulses a of relatively long duration and intervening secondary control pulses b oj/relatively short duration. By way of example, this periodic potential is shown as having equal time intervals between the leading edges of all adjacent pulses whetherthey be of the master or secondary control type. It is the purpose of the unit 25 to separate the master control pulses a from the secondary control pulses b and to apply the master control pulses a to the master control-circuit terminals 22, 23 and the secondary control pulses b to the secondary control-circuit terminals 28, 29. In eiiecting this result, fidelity of wave form of the pulses is not essential, it being only important that the steep slope of the leading edge of the pulses be largely preserved in order that control impulses shall be applied to the terminals 22, 23 and 28, 29. Such impulses are applied to these terminals with negative polarity.

Assume now thatthe first vacuum tubes I0, I, and ID" of the pairs of cascade-connected tubes included in the respective switching stages A, B and C are normally conductive and that the second tubes II, II' and II" of the switching stages are normally nonconductive. Under this condition, the first vacuum tube of the switching stage A has high transconductance and the second tube low transconductance. Further, since no space current flows through the vacuum tube II, no potentialis developed across the cathode resistor I 8 of this tube, and the vacuum tube I2 consequently is biased from the source +0 to anode current cutoff. This is true also of the switching stages B and C and, hence, none of the output circuits 3I-32, 3I' 32', or 3I"-32" of the switching stages are energized through the vacuum tubes I2, I2 and I2", respectively. Now, upon the application of a negative-polarity master-control pulse a to the control electrode of vacuum tube ID, the latter is biased by the master control pulse to anode current cutofl, thereby to apply a corresponding positive pulse to the control electrode of vacuum tube II to cause this tube to become conductive. When vacuum tube I I becomes conductive, several things occur. First, a negative potential is applied through the resistor 2I to the control electrode of vacuum I0 tobias the latter even farther beyond anode current cutoff. Secondly, a positive impulse is applied through the condenser I9'to the control electrode of vacuum tube I0 but this impulse is ineffective to change the state of conductivity of the latter vacuum tube since this tube is already in the conductive state. Lastly, the positive potential developed across the cathode resistor I8 is applied to the vacuum tube I2 t render the latter conductive. The signal applied to th inputcircuit terminals 33, 34 is thus repeated b the vacuum tube I2 to energize the output circuit comprising output-circuit terminals 3|, 32 of the switching stage A. It may be noted that the resistors I8 and-31 act as a voltage divider for sigpreciable signal voltage is applied to the input electrodes of tubes I I and I0. At the end of the master pulse a, the vacuum tube III does not again become conductive since it is maintained in a nonconductive state by the negative potential pulse applied to its control electrode through resistor 2| from the vacuum tube II.

The next pulse of the periodic potential applied to unit 25 following the master pulse is a secondary control pulse b. This pulse is separated by unit 25 and applied with negative polarity to the secondary control-circuit terminals 28, 29 and thus simultaneously is applied to the control electrodes of vacuum tubes II, II', and II. The vacuum tubes II and I I", however, are in the nonconductive state and the secondary control pulse consequently does not effect any change of the conductivity of these tubes. On the other hand, the vacuum tube II of switching stage A has been conditioned by the master control pulse applied to the vacuum tube I0 in initiating the control sequence and, being in a conductive state,

is biased by the secondary control pulse beyond anode current cutoff. When the vacuum tube I I becomes nonconductive, several things occur. In the first place, a positive potential is applied to the control electrode of vacuum tube III to cause the latter to become conductive again, the conductivity of the vacuum tubes I 0 and II thus varying in opposite senses. Secondly, a negative potential impulse is developed across the cathode resistor I8 of tube II and is applied to the control electrode of vacuum tube Ill of the switching stage B to cause the latter vacuum tube to be biased beyond anode current cutofi, whereupon the second tube I I' of this switching stage has its conductivity varied in opposite sense to that of tube II) by a positive potential impulse applied thereto from the latter tube. Tube I I' of switching stage B is thus conditioned to be responsive to the next seconda'ry control pulse. Thirdly, the positive potential developed across the cathode resistor I8 of tube II during the time the latter was conductive disappears, whereupon the bias from the source +C whichv is applied to the cathnonconductive and the signal applied to the input-circuit terminals 33, 34 is no longer repeated to the output-circuit terminals 3|, 32. This control circuit is therefore deenergized and the control-circuit terminals 3I, 32' thereupon become energized through the vacuum tube I2' by virtue of the conductive state of vacuum tube I I'.

The next secondary control pulse applied to the control-circuit terminals 28, 29 likewise is applied to the vacuum tubes II, II' and II", but since the vacuum tubes I I and I I" are now in the nonconductive state, the applied secondary control pulse has no eflect in modifying their state of conductivity. The vacuum tube II', however, is

conductive at this time and the secondary control pulse causes this vacuum tube to be biased to anode current cutoif. As in the operation of the switching stage A, vacuum tube II' upon becoming nonconductive causes the vacuum tube IIl' again to become conductive, causes the vacuum tube I0 of the switching stage C to become non-conductive and the second vacuum tube II" of this switching stage to become conductive, and, lastly, causes the vacuum tube I2 to be nonconductive. As in the switching stage A, the vacuum tube I2 of the switching stage B is effective its input-circuit terminals 33, 34' to its controlcircuit terminals 3|, 32', thus to energize the latter during this interval.

It will be evident that the'third secondary control pulse applied to the control-circuit terminals 28, 29 does not afiect the state of conductivity of the vacuum tubes H and II, which are now nonconductive, but does cause the vacuum tube II" to become nonconductive, thus rendering vacuum tube Ill" conductive and deenergizing the control-circuit terminals 3|", 32" which had been energized during the time that the vacuum' tube l I" was conductive. It will be seen that the third of the secondary control pulses completes the third successive step of the control sequence and that the control sequence described is initiated again upon the application of a master control pulse a. to the control electrode of 2|" intercouple the vacuum tubes ill-J1", in-' clusive,- in pairs to vary the conductivity of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair, Such variation of the conductivity of the tubes in opposite senses is due, of course, to the fact that the vacuum tubesof each switching stage A, B and C are coupled as direct current amplifiers in both forward and backward directions as pointed out in connection with the switching stage A. It will further be evident that the plurality of output circuits comprising outputcircuit terminals 3|-32, 3l'32', 3l"32" of the respective switching stages A, B and C are adapted successively to have their energization modified by successive secondary control impulses and that each is energized during thecycle of variation of the conductivity. of one tube of the group of tubes associated therewith, specifically, the second tube of the pair included in each switching stage. Further, it will be seen that the conductivity of at least one tube of the group of tubes included in each of the switching stages is varied through a complete cycle in response to impulses successively individually applied to two tubes of such group of tubes.

While the arrangement above described utilizes a single periodic-pulse control potential including master and secondary control pulses and also utilizes a unit 25 for separating these two types of pulses, it is to be understood that this is by way of example only. Thus, thepulses of the control potential may occur at any desired random interval and may have any desired wave form, it being only desirable that the wave form shall be such that the leading edge of each'pulse' is preferably rather steep since it is this portion of the pulse which effectively constitutes the potential impulse necessary to effect control of the stage A.

master pulse from the control-circuit terminals 22, 23 only to the control electrode of vacuum tube III of switching stage B instead of to the control electr de-of the vacuum tube 10 of switchin us, if an electronic switch of the type described includes fifteen such switching stages, for example, the same or different master control pulses may be applied simultaneously or in any desired regular or irregular order at any selected point or points along such series of switching stages to initiate several control sequences simultaneously or in a desired order. In the latter event, the secondary control pulses may be applied simultaneously to all or the switching stages, for example, concurrently to complete the plu-. rality of control sequences.

The term conductance characteristic" as used in the claims appended hereto is intended to denote the transconductance of the vacuum tubes where this factor is important, as where the vacpended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An electronic switch comprising, a plurality of vacuum tubes coupled in-cascade, means intercoupling said tubes in groups to vary through a complete cycle the conductance characteristic of at least one tube of each group in response to impulses successively individually applied to two tubes of said each group, means for conditioning one of said cascaded'tubes to initiate a control sequence, means for applying impulses to the-said conditioned tube and to a corresponding tube of each of said groups, said impulses being effective to vary the conductance characteristic of at least said one tube in each of the successive groups of saidtubes in like manner, thereby to complete successive steps of said control sequence, and a plurality of output circuits each individually. coupled to at least said first-named one tube of each of said groups and adapted successively to have the energization thereof modified during the cycle of variation of the conductance characteristic of said'first-named one tube of the group of tubes associated therewith.

2. An electronic switch comprising, a, plurality of vacuum-tube repeaters coupled in cascade, means intercoupling said tubes in groups to vary through a. complete cycle the transconductance of at least one tube of each group in response to impulses successively individually applied to two electronic switch. Further, should it be desired thatthe control sequence includes only switching stages B and C, for example, it will be evident that this may be accomplished by applying the :5

tubes of said each group, means for conditioning one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and to a corresponding tube of each of said groups, said impulses being efiective to vary the transconductance of said one tube in successive groups of said tubes in like manner, thereby to complete successive steps of said control sequence, and a plurality of output circuits each individually coupled to at least said firstnamed one tube of each of said groups and adapted successively to have the energization thereof modified during the cycle of variation of the transconductance of said first-named one tube of the group of tubes associated therewith.

3. An electronic switch comprising, a plurality of vacuum tubes coupled in cascade, means intercoupling said tubes in groups to vary through a complete cycle the conductance characteristic of at least one tube of each group in response to impulses successively individually applied to two tubes of said each group, means for applying an impulse to one of said cascaded tubes to condition another tube of the group associated therewith to initiate a control sequence, means for simultaneously applying impulses to the said conditioned tube and to a corresponding tube of each of said groups to vary the conductance characteristic of successive groups of said tubes, thereby to complete successive steps of said control sequence, and a plurality of output circuits each individually coupled to at least said first-named one tube of each of said groups and adapted successively to have the energization thereof modified during the cycle of variation of the conductance characteristic of said first-named one tube of the group of tubes associated therewith.

4. An electronic switch comprising, a plurality of vacuum tubes connected in cascade, means intercoupling said tubes in pairs to vary the con-' ductance characteristic of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair, means for conditioning one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being effective to vary the conductance characteristic of successive pairs of said tubes in like manner, thereby to complete successive steps of said controlsequence, and a plurality of output circuits individually coupled to at least one tube of each of said pairs and adapted successively to have the energization thereof modified during the cycle of variation of the conduct ance characteristic of the pair of tubes associated therewith.

5. An electronic switch comprising, a plurality of vacuum-tube repeaters connected in cascade, means intercoupling said tubes in pairs to vary the transconductance of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair, means for conditioning one of said cascaded tubesto initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being efiective to vary the transconductance of successive pairs of said tubes in like manner, thereby to complete successive steps of said control sequence, and a plurality of output circuits eachindividually coupled to at least one tube of each of said pairs and adapted successively to have the energization thereof modified during the cycle of variation of the transconductance of the pair of tubes associated therewith.

6. An electronic switch comprising, a plurality of vacuum tubes connected in cascade, means intercoupling said tubes in pairs to vary the conductance characteristic of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair, means for applying an impulse to the first tube of one of the pairs of the cascaded tubes to initiate a control sequence, means for simultaneously applying impulses to the second tube of saidone pair and alternate tubes therefrom in said cascade connection to vary the conductance characteristic of successive pairs of said tubes, thereby to and a, plurality of output circuits each individually coupled to at least one tube of each of said pairs and adapted successively to have the energization thereof modified during the cycle of variation 01. the conductance characteristic of the pair of tubes associated therewith.

'7. An electronic switch comprising, a, plurality of vacuum tubes connected in cascade, means intercoupling said tubes in pairs as direct current repeater devices to vary the transconductance of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubesof the pair, means for conditioning one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being effective to vary the transconductance of successive pairs of said tubes in like manner, thereby to complete successive steps of said control sequence, and a. plurality of output circuits each individually coupled to at least one tube of each of said pairs and adapted successively to have the energization thereof modified during the cycle of variation of the transconductance of the pair of tubes associated therewith. I

8. An electronic switch comprising, a plurality of vacuum tubes connected in cascade in a forward direction and in pairs as direct current repeater devices, means intercoupling said tubes in a backward direction in said pairs as direct current repeater devices to vary the transconductance of the tubes of each pair in, opposite senses in response to an impulse applied to either of the tubes of the pair, means ,for conditioning one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being effective to vary the transconductance of suc cessive pairs of said tubes in like manner, thereby to complete successive steps of said control sequence, and a plurality of output circuits each individually coupled to at least one tube of each of said pairs and adapted successively to have the energization thereof modified during the cycle of variation of the transconductance oi. the pair of tubes associated therewith.

9. An electronic switch'comprising, a plurality of vacuum tubes connected in cascade, resistive means intercoupling said tubes in pairs to vary the conductance characteristic of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair, means for conditioning one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being effective to vary the conductance characteristic of successive pairs of said tubes in like manner, thereby to complete successive steps of said control sequence, and a plurality of output circuits each individually coupled to at least one tube ofeach of said pairs and adapted successively to have the' energization thereof modified during the cycle of variation of the conductance characteristic of the pair of tubes associated therewith.

10. An electronic switch comprising, a plurality of vacuum tubes connected in cascade, a plurality of resistors intercoupling said tubes in pairs to vary the conductance characteristic of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair,

means for conditioning one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being eflective to vary the conductance characteristic of successive pairs oi said tubes in like manner, thereby to complete successive'steps of said control sequence, and a plurality or output circuits each individually coupled to at least one tube of each of said pairs and adapted successively to have the energization thereo! modified during the cycle of variation of the conductance characteristic of the pair of tubes associated therewith.

11. An electronic switch comprising, a plurality of vacuum tubes connected in cascade, means interc'oupling said tubes in pairs to vary the conductance characteristic of the tubes of each pair in opposite senses in response to an impulse applied to either of the tubes of the pair, means for conditioning one of said cascaded tubes to initiate a control sequence, means for applying impulses simultaneously to thesaid conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being effective-to vary the conductance characteristic of successive pairs .of said tubes in like manner, thereby to complete successive steps of said control sequence, and a plurality of output circuits each individually coupled to at least one tube of each of said pairs and adapted successively to have the energization thereof modified during the cycle of variation of the conductance characteristic of the pair of tubes associated therewith.

12. An electronic switch comprising, a plurality oi vacuum tubes connected in cascade, means intercoupling said tubes in pairs to vary the conductivity of the tubes or each pair in opposite senses in response to an impulse applied to either of the tubes of the pair, the first tube of each 0! I said pairs normally being conductive and the second tube normally being non'conductive, means for changing the normal state of conductivity of one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom plete successive steps of said control sequence,

in said cascade connection, said impulses being eilective to vary the conductivity of successive pairs of said tubes in like manner, thereby to coma an a plurality oi output circuits each individually coupled to at least one tube or each of said pairs and adapted successively to have the energization thereof modified during the cycle or variation 01' the conductivity of the pair of tubes associated therewith.

13. An electronic switch comprising, a plurality of vacuum tubes connected in cascade, means intercoupling said tubes in pairs to vary the conductivity of the tubes or each pair in opposite senses in response to an impulse applied to either or the tubes of the pair, the first tube of each of said pairs normally being conductive and the second tube nonnally being nonconductive, means for changing the normal state of conductivity of one of said cascaded tubes to initiate a control sequence, means for applying impulses to the said conditioned tube and alternate tubes therefrom in said cascade connection, said impulses being efiective to vary the conductivity 0! successive pairs of said tubes in like manner, thereby to complete successive steps of said control sequence, and a plurality of output circuits individually coupled to the said second tube or said pairs and adapted successively to have the energization thereof modified during the cycle of variation of the conductivity of the pair of tubes associated therewith.

JOHN KELLY JOHNSON. REFERENCES- CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Electronics, Aug. 1939, pp. 14-17, Trigger circuits, by Reich. 

